Race Classes (in their words):
Chopper: For choppers! Not factory customs or baggers, just choppers.
Street Tracker/Street Scrambler: Road-legal street trackers and scramblers, not racebikes or modern enduros.
Inappropriate Road Bike: Harley Fat Boys, Trail 90s, Ducati Panigales, virtually any road bike. If it shouldn't be on a dirt track, it's in.
Lady: Women racers on any of the above bikes (not real racebikes, please). Women can enter any other class if they prefer.
Tripod: Three-wheelers (and snowmobiles, of course)
Minibike: Pull-start 'Taco style and three-speed autos only.
Hooligan: 750-plus cc multi-cylinder beasts.